Roller vane pump with angular ranges of approximate concentric circular paths for the rollers

ABSTRACT

A fluid supply pump such as a roller cell pump which includes a multiplicity of individual pumping bodies or rollers held in the grooves of a driven rotor in contact with an eccentrically disposed roller path which, in a certain angular range around the narrowest and widest gap, it is, at each location, virtually identical with a concentric circular path which is drawn around the rotor center point, the path preferably formed by two ellipse halves, for the elliptic shape can be virtually exactly approximated around the apex points of the ellipse by means of its primary circles of curvature to thereby improve the dynamic sequence of operations, for example to increase the sealing effect of the radial gap and to adapt the expansion and compression phases to the opening and closing conditions of the intake and pressure grooves.

This is a continuation of copending application Ser. No. 566,954 filedDec. 28, 1983, now abandoned, which is a continuation of Ser. No.053,586 filed June 29, 1979, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to a supply unit for fluids. Supply units forfluids, such as the roller cell pumps which are frequently used forsupplying fuel under pressure, are known in a variety of types. As inFIG. 1, which shows the known prior art illustrated in schematicfashion, such pumps include a rotor disc or grooved disc 1 havingreception grooves 2 distributed about its circumference in which arelocated positive-displacement bodies 3. These bodies 3 may be formed asrollers, which are guided and slide in the grooves 2 and which contactan external roller path 4; the path 4 is of circular shape like thecircumference of the grooved disc 1 but is, however, eccentricallyshifted by a certain given distance at its center, so thatcrescent-shaped pumping work chambers are created which travel about thecircumference of the system and supply the induced fluid, such as fuel,to an external groove 13 and, via the play between the roller andreception element to an internal pressure groove 10 while the fluid tobe supplied or the rotor disc 1 rotates along the arrow A in itseccentric displacement with respect to roller path 4. Because of theeccentricity, a widest gap WS between the roller path 4 and the jacketsurface of the rotor and a narrowest gap ES result, which gaps naturallyare periodically traversed by the rollers 3 in their grooves upon therotation of the driven rotor.

In order to understand the present invention, it is necessary also toexplain the functional sequence of a known roller cell pump to a certainextent, with the aid of FIGS. 2a through 2c and FIGS. 3a through 3e andthe individual working phases represented thereby in order, thus, toclarify the disadvantages inherent therein.

In FIG. 1, the following references are also given, which appear as wellin the working phases of FIGS. 2 and 3. V₁ and V₂ indicate,respectively, the chamber under roller 3₁ and 3₂ ; the crescent-shapedchamber between rollers 3₁ and 3₂ and that between rollers 3₂ and 3₃ aredesignated V₃ and V₅, respectively. The pressure side, extending in eachcase from the uppermost roller which has passed with widest gap WS,toward the bottom on the left-hand side of the system shown in FIG. 1,is marked D, and the intake side is marked S.

First, the buildup of pressure at the widest gap WS will be described invarious working phases with the aid of FIGS. 2a through 2c; for the sakeof simplification, a supply medium free of bubbles, such as fuel, isassumed. In FIG. 2a, the roller 3₁ separates the intake chamber S, inwhich intake pressure prevails, from the chamber V₁ under the roller 3₁and from the crescent-shaped chamber V₃ between the rollers 3₁ and 3₂. Abuildup of pressure has not yet occurred in chambers V₁ and V₃ ; thus,intake pressure also prevails in chambers V₁ and V₃. The forwardmostedge 8 of the chamber V₁ has not yet reached the overlap area of theprotruding chamber portion 9 of the internal pressure groove 10, inwhich, as in the pressure chamber 11 and the crescent-shaped chamber V₅located in front of the roller 3₂, operational pressure prevails. Thedistance of the forward edge 8 from the protruding area 9 of thepressure groove 10 amounts to approximately 10°, as shown.

Within the next 3°, that is, at a distance of 7° between the two parts 8and 9, a substantial pressure buildup (compression) results in theclosed chamber comprising V₁ and V₃, as a result of the reduction involume of chamber V₃ (FIG. 2b). Within these 3°, a substantial pressurepeak of over 10 bar can occur in this chamber V₁ plus V₃, as a result ofwhich, roller 3₂ lifts from its previous contact at the rearward grooveedge (as seen in the direction of rotation. As a result, there is aconnection of the crescent-shaped chamber V₃ and chamber V₁ with thepressure chamber over the area through which the arrow B extends. Thechamber V₁ under the roller 3₁ is, as may be seen, not yet directlyconnected with the pressure groove 10.

Only in the working phase shown in FIG. 2c are both the crescent-shapedchamber V₃ and the chamber V₁ first connected with the pressure chamber11 via the pressure groove 10, whereby the fluid, displaced out of thechamber V₃, flows past the rollers 3₁ and 3₂ into the pressure chamberin accordance with arrows B and B'.

The working phases shown in FIGS. 3a through 3e show the pressureconditions and the sealing at the narrowest gap ES with pumping bodiesor rollers 3₁, 3₂ and 3₃, in the meantime, having traveled farther inthe rotary direction. As may be seen, the intake chamber or intakespheroid 12 extends nearly to the narrowest gap ES and, in the workingphase shown in FIG. 3a, is already connected with the chamber located inthe area of roller 3₃. At this point, the crescent-shaped chamber V₃ isconnected as indicated by arrow C with an external pressure groove 13whereby the fluid displaced out of the crescent-shaped chamber V₃ flowsvia the external pressure groove 13 and, according to arrow E, past theroller 3₂ via the inner pressure groove 10 into the pressure chamber 11.The gap width at the narrowest gap ES determines the leakage quantityoverflowing out of the crescent-shaped chamber V₅ formed between rollers3₃ and 3₂ and into the intake chamber. In the crescent-shaped chamberV₅, operational pressure prevails.

In the working phase of FIG. 3b, the connection from chamber V₂ underroller 3₂ via the inner pressure groove 10 to the pressure chamber 11 isinterrupted, for the groove bottom area 14 at that point is just leavingthe inner pressure groove 10. The fluid displaced out of chamber V₂ andthe crescent-shaped chamber V₃, which is becoming narrower and narrower,flows via the external pressure groove 13 according to arrow F into thepressure chamber, whereby chamber V₅ is still connected via the externalpressure groove 13 with the pressure chamber and a leakage quantitycontinues to overflow into the intake chamber area.

Only in the working phase of FIG. 3c is the chamber V₅ first separatedby the roller 3₂ from the external pressure groove 13 whereby thepressure in chamber V₅ rapidly drops as a result of the quantity ofoverflow across the narrowest gap ES. Roller 3₂ is pressed by theoperational pressure in chamber V₂ and the crescent-shaped chamber V₃against the forward groove edge, as shown at reference numeral 15, andthus seals off chambers V₂ and V₃ from chamber V₅. From this moment, theleakage quantity at the narrowest gap is no longer determined by the gapwidth of distance but rather by the remaining volume of chamber V₅whereby the fluid, further displaced out of chambers V₂ and V₃, flowsvia the external pressure groove 13 into the pressure chamber 11.Between groove 13 and chamber 11, there is a connection which is notshown.

In the working phase of the parts in FIG. 3d, the roller 3₂ seals offchambers V₂ and V₃ from the intake chamber at the narrowest gap, becausethe roller 3₂ continues in contact with the forward groove edge. Fromthis point on, the chamber V₂ under the roller 3₂ becomes larger,because the roller 3₂, with the roller path growing increasingly distantfrom the rotor, moves farther and farther out of its groove.Simultaneously, the gap 16 between the rear groove edge and the rollerpath grows smaller and smaller and finally reaches the gap distanceestablished by the narrowest gap ES.

The operational pressure available in chamber V₂ then drops as well,when the quantity flowing from chamber V₃ toward chamber V₂ is smallerthan the volumetric increase of chamber V₂ resulting from the furtherrotation of the rotor.

In the working phase of the parts as shown in FIG. 3e, the rear grooveedge is at the narrowest gap ES and the gap between groove edge 17 androller path has reached the minimum. As seen on the leakage quantityflowing through the narrowest gap ES is smaller than the volumetricenlargement of chamber V₂, the roller 3₂ lifts from the forward grooveedge at 18 and the pressure in chamber V₂ drops practically at once tothe lesser intake pressure, or below. The difference between theparticular groove volume and the roller volume each time a rollertraverses the narrowest gap ES is the so-called clearance volume, whichis reduced upon traversal of the narrowest gap ES from the operationalpressure to the intake pressure.

In such a supply pump for fluids having an eccentric, circular rollerpath, difficulties arise which may be quite substantial as a result ofthe lack of sealing at the narrowest gap and as a result of unfavorableexpansion and compression relationships after the narrowest gap ES andbefore the widest radial gap WS, particularly (with respect to a fuelsupply pump) during so-called hot-gasoline operation.

Since the sealing point between the pressure chamber D and the intakechamber S is formed only by a jacket line having the desired radial play(ES) of a few μm and, as explained above, the distance between the rotorand the roller path rapidly increases with increasing distance from thenarrowest gap ES, a large quantity of fuel can flow back from thepressure side to the intake side and there cause functionalinterruptions as a result of volatilization, particularly duringhot-gasoline operation.

The beginning of the intake spheroid 12 must also not be brought tooclose to the narrowest gap ES, because otherwise a direct connectioncould result between the pressure side and the intake side as a resultof a shortcut via the roller groove in the rotor disc. However, this hasthe result that, after the narrowest gap, there is an expansion of thesealed chamber volume which, until the intake spheroid is opened, thatis, until the intake spheroid 12 is reached, can cause significantunderpressures, so that the return flow of fuel and its volatilizationare still further encouraged.

Furthermore, at the closing of the intake spheroid 12 before the widestgap WS (see FIGS. 2a-2c), that is, when a particular roller area leavesthe intake spheroid area, a compression phase has already occurred forthe external partial chamber volume between the rotor and the rollerpath, while, in contrast, the inner partial chamber volume in the rollergroove enlarges still further, which can also have undesirable effects.

There is accordingly a need for a supply unit for fluids whose basicconcept corresponds to a roller cell or vane cell pump and in which thedisadvantages of the known eccentric circular roller path which aredescribed above are avoided, that is, in which the sealing effect of theradial gap is increased and the expansion and compression phases areadapted to the opening and closing conditions of the intake and pressurespheroids.

OBJECT AND SUMMARY OF THE INVENTION

The supply unit for fluids constructed in accordance with the inventionhas the advantage over the prior art in that the radial play between theroller path and the grooved disc which is adjustable by means ofdisplacement of the intermediate plate which forms the roller path in aninterior bore--that is, generally stated, the radial play which isadjustable by means of a relative displacement between the intermediateplate and the rotor or grooved disc--can be kept approximately constantover a large angular range before and after the narrowest gap in theform of the roller path in accordance with the invention, in fact, overa range of approximately ±20° before and after the narrowest gap. Thispermits the attainment of a substantially better sealing effect comparedwith that in an eccentric, circular roller path in which the radial playprogressively increases with the distance from the narrowest gap.

By means of the transition of the roller path approximating a circularcontour concentric with the center of the rotor or grooved disc, thecompression phase of the pumping chamber can be terminated quite adistance before the narrowest gap. The closing of the pressure groovecan then occur earlier, whereby, in an analogous manner the expansion ofthe particular pumping chamber is initiated later after the narrowestgap and therefore the intake groove can, accordingly, be opened later.

It is particularly advantageous that the very marked underpressureformation which results from the expansion of the chamber volume afterthe narrowest gap before the intake groove is opened can, to a greatextent, be avoided.

At the widest gap, that is, at the transition from the intake to thepressure side, the approximately circular path of the roller path, whichis also concentric with the center of the rotor, means that the intakespheroid can be closed at such a time when both the exterior partialchamber volume and that volume located under the roller have bothalready terminated their expansion phase. As a result, the course overtime of the compression in the region of the negative overlap (that is,when the crescent-shaped chamber V₃ and chamber V₁ under the roller areconnected neither to the pressure side nor the intake side) can beaccomplished with a more gradual transition.

In addition, a more gradual process of compression results as the pumpcontinues to rotate further.

The previously referred to relatively high pressure peaks resulting fromcompression of the fluid in the chamber volume which is entirely closedoff at a rotary angle of 10° (see FIGS. 2a-2c) may be entirely preventedby means of an appropriate positioning of the control edges; that is,this 10° range is so located that it coincides with the angular range inwhich no compression, or an extremely limited amount of compression,takes place. In addition, this can result in a reduction in noise,because the severe pressure fluctuations which permit a fluctuation ofthe supply medium are reduced.

In addition, with particular reference to a roller cell pump, there isan additional protection against pressure peaks, even when the peakshave already been reduced to a certain extent automatically by means ofappropriate roller movements.

In vane cell pumps, where such a self-regulating function is not presentand where previously such pressure peaks could be reduced only viacompression oil grooves or bores, this effect of a "braked" compressionsignifies a decisive improvement.

It is particularly advantageous that the requirement for a concentric,approximately circular course of the roller path about the center of thegrooved disc or rotor can be very well accomplished in that the rollerpath can be composed of two ellipse halves. Then the elliptical shapecan almost exactly be obtained in the area of the apex points whichapproximate primary circles of curvature.

The invention can be realized without comparatively great expensebecause the centers of the two ellipse halves are identical and,furthermore, the rotor center is not identical with the centers of theparticular primary circles of curvature of the ellipses.

The invention will be better understood as well as further objects andadvantages thereof become more apparent from the ensuing detaileddescription of the preferred embodiment taken in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a well-known roller cell pump;

FIG. 2a is a schematic illustration similar to FIG. 1 of a portion of awell-known roller cell pump relating to the function and pressurebuildup at the widest gap in a first working phase;

FIG. 2b is a view similar to FIG. 2a of a second working phase of awell-known roller cell pump;

FIG. 2c is a view similar to FIG. 2a of a third working phase of awell-known roller cell pump;

FIG. 3a is a schematic illustration of the lower portion of the rollercell pump of FIG. 1 illustrating the pressure conditions and thesealings at the narrowest gap in a first working phase;

FIG. 3b is a view similar to FIG. 3a showing the parts in a secondworking phase;

FIG. 3c is a schematic illustration similar to FIG. 3a showing a thirdworking phase of the parts;

FIG. 3d is a schematic illustration similar to FIG. 3a showing the partsin a fourth working phase;

FIG. 3e is a schematic illustration similar to FIG. 3a showing the partsin a fifth working phase; and

FIG. 4 is a schematic showing of the roller path for the supply pump ofthe invention operating on the basic principle of a roller piston pumpin which the rollers follow a pump inner chamber having a non-circularcontour.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The basic concept of the present invention is to improve the operationof fluid supply pumps, particularly during hot operation of the mediumto be supplied, i.e., in a fuel supply pump, during hot-gasolineoperation. By means of a new embodiment of the roller path disposedeccentrically relative to the rotor, with the roller path being soformed that it is virtually, and, from the practical standpoint,approximates a circular course which extends, in a certain angular rangeabout the narrowest and the widest gap, concentrically about the rotorcenter; that is, about the center of the grooved disc or rotor discwhich receives the pumping bodies or rollers in grooves.

As shown in FIG. 4, the rotor or grooved disc center point is indicatedat M. From this center M, the radius R₂ of the rotor extends which, inrotating about the center M, defines the jacket line of the grooved discwhich is shown in broken lines in FIG. 4 and indicated by the referencenumeral 20.

In the known circular roller cell pump, there is a center point M',disposed at a distance e_(kr) and thus eccentrically with respect to thecenter M of the eccentric circular contour of the known roller path 21having the radius R₁, which path 21 extends as a circle about the centerM' and is depicted in FIG. 4 by a fine line.

The invention departs from the above described arrangement in that inorder to form the roller path in accordance with the invention, which isshown in FIG. 4 and depicted by a heavy line and identified by thereference numeral 22, the roller path is divided into two halves, anupper half 22a, which comprises somewhat less than a "semicircle" and at23 and 24 turns into a lower half 22b, which is somewhat larger than a"semicircle". The upper and lower halves 22a, 22b formed respectively byradius vectors ρ₁ (φ) (referring to the upper half 22a) and ρ₂ (φ)(referring to the lower half 22b) extending about the center M of thegrooved disc, the length of these radius vectors being a function of theangle φ.

In the illustrated embodiment, the ellipse halves 22a and 22b form theroller path for the rollers of the rotor of the pump, which, placedtogether with transition points at 23 and 24, form the roller path inaccordance with the invention. Because the ellipse shape can bevirtually exactly approximated in the area of the apex points WS and ESby means of their primary circles of curvature which follow thecurvature of a circle in the area of WS and ES as shown by the thin linecircle 21 having a center M', this embodiment of a roller path inaccordance with the invention fulfills extraordinarily well the basicconcept of the present invention as it has been defined above namely,within a certain angular range about the narrowest and widest gap to beapproximately identical with a concentric circle about the rotor center.The narrowest gap is shown between the rotor and the roller path at ESand the widest gap is shown between the rotor and the roller path at WS.

The centers of the two ellipse halves are identical and in FIG. 4 aredesignated M_(e). The rotor center M is identical with the centers ofrespective circles of curvature which centers at M which practicallyidentically represent the ellipse shape in the area of the apex pointsWS and ES. That is, a circular arc with radius R2 will substantiallycoincide with the ellipse 22b beginning on opposite sides of ES and acircular arc with radius R2+S2 will substantially coincide with ellipse22a beginning on opposite sides of WS.

In other words, based on the foregoing it will be understood that inthis structure the roller path formed by the two elliptical halves,having the same geometrical center Me disposed eccentrically to thegrooved disc 20 for contact by the rollers is arranged so that theellipse shape about the apex points WS and ES of the ellipse halvesrepresent approximate circular arcs.

There is a distance S₂ between the ellipse center M_(e) and the rotorcenter M which is produced by the need for sufficient overlapping of thegroove edge with the roller jacket line contacting it.

As seen in FIG. 4 a roller vane pump is formed with an internal casingsurface 22 formed by two ellipse halves 22a and 22b having a geometricalcenter Me and joined at their ends 23 and 24. The transition from oneellipse half to the next ellipse half has a relatively smooth transitionat their joints 23 and 24 because the surfaces so formed aresubstantially circular arc sections as shown by the circle 21 whichcoincides with the ellipse halves at 23 and 24 and at the apex ends ofthe ellipse halves at WS and ES. The smooth roller path formed by theellipse halves defines a contact surface for the peripheral rollers ofthe rotor having a center M. The rotor axis is mounted off center fromthe center of the roller path so that the narrowest point between therotor and the roller path is at ES and the widest point between therotor and the roller path is at WS. As seen from the drawing, the rotorcenter M is not the same as the centers Me of the ellipse halves. Thegeometric center Me of the two ellipse halves are not identical with thecenter point M of the rotor. The path formed by the ellipse halves areellipital with respect to their geometrical centers Me; however, theelliptical path approximates a circular arc along the portion at WS andES with radii coinciding with the center M of the rotor. Therefore, theellipse halves approximate a circular arc with respect to the center ofthe rotor disc when their centers coincide with the center M of therotor.

The major semi-axis a₁ of the upper ellipse half is identical to theminor semi-axis b₂ of the lower ellipse half. The constant radius of theprimary circle of curvature of the lower ellipse half 22b at EScorresponds to the constant radius R₂ of the rotor disc. For the upperhalf 22a, the radius of the circle of curvature is equal to the rotorradius R₂ plus the center point displacement S₂ at WS. This can beeasily seen with the aid of the following equations for the roller path,expressed in polar coordinates. For the radius ρ₁ dependent on the angleφ and therefore variable, the following equation results: ##EQU1## whereρ₁ lies between the limits of ##EQU2##

The equation for the lower path or ellipse half 22b results in: ##EQU3##where ρ₂ lies between the limits of ##EQU4##

The two radii ρ₁ and ρ₂ dependent on the angle φ are each identical atthe transition points 23 and 24, as can readily be ascertained byinserting numerical values into the two equations (1) and (2), so that aroller path results having a continuous transition.

The following Table I shows the calculated radii, varying in accordancewith the angle φ, of both roller path halves 22a, 22b as an embodimentof the invention although it should be understood that the invention is,of course, not limited to this. The calculated values, however,demonstrate particularly well the advantages which result in thepractical operation of a roller cell pump or a comparable unit on thebasis of the roller path in accordance with the invention.

The following values are the basis for the calculation:

    R.sub.2 =15 mm

    S.sub.2 =2 mm

while in FIG. 4, on the same scale, R₁ has a value of 16 mm and theeccentric distance e_(kr) amounts to 1 mm.

                  TABLE I                                                         ______________________________________                                        1                2                                                            ______________________________________                                         0°                                                                           17.000    360°                                                                           82.86   16.094                                                                              277.14                                  2     "         358     84      16.054                                                                              276                                     4     "         356     86      15.986                                                                              274                                     6     "         354     88      15.921                                                                              272                                     8     "         352     90      15.858                                                                              270                                    10     17.000    350     92      15.797                                                                              268                                    12     16.999    348     94      15.740                                                                              266                                    14     16.999    346     96      15.684                                                                              264                                    16     16.998    344     98      15.632                                                                              262                                    18     16.997    342     100     15.581                                                                              260                                    20     16.996    340     102     15.534                                                                              258                                    22     16.994    338     104     15.489                                                                              256                                    24     16.991    336     106     15.446                                                                              254                                    26     16.988    334     108     15.406                                                                              252                                    28     16.984    332     110     15.368                                                                              250                                    30     16.979    330     112     15.332                                                                              248                                    32     16.973    328     114     15.299                                                                              246                                    34     16.966    326     116     15.268                                                                              244                                    36     16.958    324     118     15.239                                                                              242                                    38     16.948    322     120     15.213                                                                              240                                    40     16.936    320     122     15.188                                                                              230                                    42     16.923    318     124     15.166                                                                              236                                    44     16.908    316     126     15.145                                                                              234                                    46     16.891    314     128     15.126                                                                              232                                    48     16.872    312     130     15.109                                                                              230                                    50     16.850    310     132     15.094                                                                              228                                    52     16.826    308     134     15.080                                                                              226                                    54     16.800    306     136     15.068                                                                              224                                    56     16.771    304     138     15.057                                                                              222                                    58     16.739    302     140     15.047                                                                              220                                    60     16.704    300     142     15.039                                                                              218                                    62     16.667    298     144     15.032                                                                              216                                    64     16.626    296     146     15.025                                                                              214                                    66     16.582    294     148     15.020                                                                              212                                    68     16.536    292     150     15.016                                                                              210                                    70     16.486    290     152     15.012                                                                              208                                    72     16.433    288     154     15.009                                                                              206                                    74     16.377    286     156     15.007                                                                              204                                    76     16.318    284     158     15.005                                                                              202                                    78     16.256    282     160     15.003                                                                              200                                    80     16.191    280     162     15.002                                                                              198                                    82.86  16.094    277.14  164     15.001                                                                              196                                                             166     15.000                                                                              194                                                             168     "     192                                                             170     "     190                                                             172     "     188                                                             174     "     186                                                             176     "     184                                                             178     "     182                                                             180     15.000                                                                              180                                    ______________________________________                                    

The dependence of the radius vectors ρ₁ and ρ₂ defining the twodifferent elipse halves on the angle φ, at intervals of 2 degrees ofangle at a time, may be drawn from the table, whereby at an angleφ=82,86°, there is identity of radius vector ρ₁ with radius vector ρ₂.One moves therefore from the angle 82,86° over from radius ρ₁ to radiusρ₂ and allows the angle φ₂ for the lower ellipse half 22b to continue onfrom 82,86° up to 277.14°, corresponding to the transition point 24, atwhich then the radius ρ₂, having a numerical value according to thetable of 16.094, again turns into the radius ρ₁ of the upper ellipsehalf.

From the table it can be seen that ρ₁ is practically constant at fourpoints for an angle φ₁ =±20° in the area of φ₁ =0. The same can be seento occur for the numerical value of 15.00 for ρ₂ in the range of180°±20°. A course of the roller path of this sort about the widest gapWS and the narrowest gap ES is particularly advantageous, as acomparison of the circular courses of rotor disc 20 and circular rollerpath contour 21 (broken and fine lines; known embodiment forms) shows,which narrow sharply toward the narrowest gap ES and widen out againthereafter, with the conditions which make possible a virtual identityof the roller path according to the invention already more than 20°before the narrowest gap and more than 20° after the narrowest gap, withrespect to the circular form of the rotor disc.

In this area, before and after the narrowest gap ES (and analogouslyapplied to the widest gap WS), there is practically no noticeable volumechange any longer between the roller path and the grooved disc or rotorjacket, so that here as well no volume displacements can arise whichwould lead to extreme operating conditions. Still, the roller path inaccordance with the invention has practically the same volume-distancerelationships, albeit shifted, with the rotor disc, because what ismissing, for example, as a very small crescent-shaped chamber 25 in thethird quadrant (first forward half of the lower ellipse half 22b)appears as a supplementary chamber 25' in the second quadrant, while theapproach of the roller path to the jacket surface of the rotor disc isgreatest approximately in the area of 26 and takes a substantiallysteeper course than in a known, concentric circular roller path.However, this "compression phase" is already terminated long before thenarrowest gap; corresponding conditions are found at all the criticaltransition areas described above, so that the overall result in asubstantially gentler, more gradual operation, braked compression, andprotection from pressure peaks as well as from the increased wear andpossible fluctuations which pressure peaks cause.

The foregoing relates to a preferred embodiment of the invention, itbeing understood that other embodiments and variants thereof arepossible within the spirit and scope of the invention, the latter beingdefined by the appended claims.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. A supply unit for fluids, in particular a fuelsupply pump in the form of a roller cell or vane cell pump which isdisposed in a common housing with a driving electromotor comprising, incombination, a driven rotor disc having a plurality of grooves, aplurality of individual pumping rollers disposed in said rotor discgrooves, a roller path formed by two ellipse halves having the samegeometrical center Me disposed eccentrically to said disc for contact bysaid rollers, the major semi-axis of one ellipse half being identical tothe minor semi-axis of the other ellipse half, whereby the ellipse shapeabout the apex points WS and ES of said ellipse halves approximatecircular arcs of curvature with centers coinciding with said rotor disc,said roller path within an angular range of ±20° about the narrowest andwidest gap distances at the apex of said ellipical halves beingsubstantially identical in each area with a concentric circular pathabout the center of said rotor path.
 2. A supply unit in accordance withclaim 1, wherein the radius of the approximate circular arc of curvatureof the lower ellipse half corresponds to the radius of said rotor discand wherein the radius of the approximate circular arc of curvature ofthe upper ellipse half is equal to the radius of said rotor disc plusthe center point displacement between the center of said rotor disc andthe center of said ellipse halves.
 3. A supply unit in accordance withclaim 2, wherein the radii (ρ₁, ρ₂) of the two ellipse halves formingsaid roller path are a function of an angle (φ) whereby the two radii attwo transition points are identical and have their center point in thecenter point of said rotor disc.
 4. A supply unit in accordance withclaim 1, wherein the radii (ρ₁, ρ₂), expressed in polar coordinateshaving the center point in the center point of said rotor disc, of theroller path composed of two ellipse halves follows the followingequations: ##EQU5## where ρ₁ lies between the limits of ##EQU6## whereρ₂ lies between the limits of ##EQU7## wherein R2 is the constant radiusof said rotor disc and S2 is the distance of the ellipse center point(M_(E)) from the rotor disc center point (M).
 5. A supply unit inaccordance with claim 3, wherein in addition to the identity of the tworadii (ρ₁, ρ₂) at the transition of points, the slopes, that is, thefirst derivatives of the functions representing the curve, are alsoidentical at said transition points.
 6. A supply unit in accordance withclaim 1 wherein radii (ρ₁, ρ₂), expressed in polar coordinates havingthe center point in the center point of said rotor disc, of the rollerpath composed of two ellipse halves follows the following equations:##EQU8## where ρ₁ lies between the limits of ##EQU9## where ρ₂ liesbetween the limits of ##EQU10## wherein R2 is the constant radius ofsaid rotor disc and S2 is the distance of the ellipse center point(M_(E)) from the rotor disc center point (M).
 7. A supply unit inaccordance with claim 2 wherein radii (ρ₁, ρ₂), expressed in polarcoordinates having the center point in the center point of said rotordisc, of the roller path composed of two ellipse halves follows thefollowing equations: ##EQU11## where ρ₁ lies between the limits of##EQU12## where ρ₂ lies between the limits of ##EQU13## wherein R2 isthe constant radius of said rotor disc and S2 is the distance of theellipse center point (M_(E)) from the rotor disc center point (M).
 8. Asupply unit in accordance with claim 3 wherein radii (ρ₁, ρ₂), expressedin polar coordinates having the center point in the center point of saidrotor disc, of the roller path composed of two ellipse halves followsthe following equations: ##EQU14## where ρ₁ lies between the limits of##EQU15## where ρ₂ lies between the limits of ##EQU16## wherein R2 isthe constant radius of said rotor disc and S2 is the distance of theellipse center point (M_(E)) from the rotor disc center point (M).